It is widely thought that intracranial saccular aneurysms rupture when wall stress exceeds wall strength. Yet, the rupture-potential of these lesions is still judged primarily by their maximum dimension, which of course does not explain why some small lesions rupture whereas many larger ones do not. The underlying hypothesis of this proposal is that it is the 3-D geometry, material properties and loading conditions--not the maximum dimension--that governs the rupture-potential of saccular aneurysms. Because every lesion is biomechanically unique, however, it is unreasonable to expect that statistics alone can delineate improved predictors of rupture-potential based on pathological examinations or clinical studies. Rather, there is a need to first identify specific characteristics that are the determinants of rupture, and thereby identify classes of lesions for statistical comparisons. Toward this end, we will be the first to: (1) measure the regional, multiaxial mechanical properties of human saccular aneurysms, (2) correlate these properties with the underlying 3-D collagen orientations and cross-linking, and (3) perform literally hundreds of numerical experiments that will identify those parameters (e.g., lesion size, 3-D shape, thickness, stiffness, anisotropy, heterogeneity, loading conditions, etc) that give rise to the highest multiaxial stresses (particularly in the fundus where rupture tends to occur), and by inference, the highest rupture-potential. Our results will thereby provide much needed guidance for future statistically-based retrospective and prospective studies wherein rupture can be correlated directly with clinically measurable lesion characteristics. Our research is an essential means, not an end, toward rational management of unruptured aneurysms.